Schellenberger owned a painting and decorating store in Stratford before entering political life. Schellenberger also served as a volunteer firefighter with the Perth East Fire Department for 14 years. He is a freemason, and an elder at Avonton Presbyterian Church.

In 1996 Schellenberger raised $26,000 for the Sebringville Community Center and the Sebringville Athletic Association by walking from Tobermory to Sebringville.

Richardson resigned his seat on November 10, 2002, suffering from a terminal illness. The subsequent by-election in 2003 garnered national attention, as both the Progressive Conservative and Canadian Alliance candidates attempted to displace the governing Liberals in the riding. Schellenberger, still running as a Progressive Conservative, defeated Liberal Brian Innes by 1,001 votes; despite several appearances from party leader Stephen Harper, the Alliance candidate, Marian Meinen, finished a distant third.[1] Many interpreted this as a sign that the Alliance would be unable to win many Ontario seats in the next election. Shortly after his election, Schellenberger endorsed Peter MacKay for the leadership of the Progressive Conservative Party.

Schellenberger was appointed Deputy Whip of the Progressive Conservative Party in September 2003. In early 2004, the Progressive Conservative and Canadian Alliance parties merged as the Conservative Party of Canada.

In the federal election of 2004, Schellenberger was elected to the newly created riding of Perth-Wellington. He defeated Innes by almost 4,000 votes.

In the 2006 federal election, Schellenberger was re-elected by a margin of 9,703 votes, defeating the Liberal candidate, David Cunningham. In the 39th Canadian Parliament, Schellenberger was elected Chair of the House of Commons Standing Committee on Canadian Heritage.

In the 2008 federal election, Schellenberger won Perth-Wellington for a third time with 20,765 votes (48.08% of valid ballots) defeating Liberal challenger Sandra Gardiner by 10,540 votes.[2] NDP candidate Kerry McManus finished third. In the 40th Canadian Parliament Schellenberger again served as Chair of the House of Commons Standing Committee on Canadian Heritage. In November 2010 Schellenberger became chair of a second House of Commons committee, the Standing Committee on Veterans Affairs.

In the 2011 federal election, Schellenberger won Perth-Wellington for a fourth time with 25,281 votes (54.5% of valid ballots) defeating NDP candidate Ellen Papenburg (9,861 votes) and Liberal candidate Bob McTavish (8,341 votes). In the 41st Canadian Parliament Schellenberger serves as a member of the Standing Committee on Foreign Affairs and International Development as well as the Subcommittee on International Human Rights.

Schellenberger also serves as Chair of the Canada-Germany Interparliamentary Group. In July 2014 he hosted German Ambassador Werner Wnendt in his riding.[3]